PK-Sim® uses building blocks that are grouped into Individuals, Populations, Compounds, Formulations, Administration Protocols, Events, Observers and Observed Data. The different building blocks are described in detail in “Working with PK-Sim®”. Building blocks from these groups are combined to produce a model. The advantage of building blocks is that they can be reused. For example, after having established a model for a drug after single dose intravenous administration to an animal species, just substitute the individual by a suitably parameterized virtual human population and obtain a first in man simulation model. Further substitute the formulation, to obtain a controlled-release per oral simulation model, substitute the protocol to a obtain a multiple dose simulation model, or substitute the compound to obtain a simulation model for another drug.